Electrochemical Epoxidation of Propylene to Propylene Oxide via Halogen-Mediated Systems

As one of the most important derivatives of propylene, the production of propylene oxide (PO) is severely restricted. The traditional chlorohydrin process is being eliminated due to environmental concerns, while processes such as Halcon and hydrogen peroxide epoxidation are limited by cost and efficiency, making it difficult to meet market demand. Therefore, achieving PO production through clean and efficient technologies has received extensive attention, and halogen-mediated electrochemical epoxidation of alkene is considered to be a desirable technology for the production of alkylene oxide. In this work, we used electrochemical methods to synthesize PO in halogen-mediated systems based on a RuO₂-loaded Ti (RuO₂/Ti) anode and screened out two potential mediated systems of chlorine (Cl) and bromine (Br) for the electrosynthesis of PO. At a current density of 100 mA·cm^-2, both Cl- and Br-mediated systems delivered PO Faradaic efficiencies of more than 80%. In particular, the Br-mediated system obtained PO Faradaic efficiencies of more than 90% at lower potentials (≤1.5 V vs RHE) with better electrode structure durability. Furthermore, detailed product distribution investigations and DFT calculations suggested hypohalous acid molecules as key reaction intermediates in both Cl- and Br-mediated systems. This work presents a green and efficient PO production route with halogen-mediated electrochemical epoxidation of propylene driven by renewable electricity, exhibiting promising potential to replace the traditional chlorohydrin process.